ARS | Publication request: Salmonella prevalence in “first pull” versus “close out” market pigs

Submitted to: American Association of Swine Veterinarians Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: December 6, 2006
Publication Date: March 3, 2007
Citation: Rostagno, M.H., Hurd, S., Mckean, J. 2007. Salmonella prevalence in “first pull” versus “close out” market pigs. American Association of Swine Veterinarians Annual Meeting. p. 77-78.

Technical Abstract: This study was designed to compare the Salmonella prevalence in the first group of pigs selected for slaughter (i.e., “First pull”) versus the last group of pigs selected for slaughter (i.e., “Close out”) from typical commercial finishing barns containing 800 - 1,000 animals. Nine paired observations were included in the study. Each paired sampling consisted in matched groups of pigs from the same barn as the “first pull” and the “close out” with a 4-week interval between groups. From each group, individual fecal samples (n = 45) and meat samples (n = 50) were collected, on-farm and at slaughter, respectively. In the laboratory, fecal samples were selectively enriched, and analyzed for the presence of Salmonella by a commercially available antigen-capture ELISA. Meat samples were kept frozen until processed, and then thawed, when the resulting liquid (“meat juice”) was collected and analyzed for the presence of antibodies against Salmonella by a commercially available indirect ELISA. All lots of pigs housed in the finishing barns studied were Salmonella-positive, based on sampling from “first pull” and “close out”. In 7/9 (77.8%) of the studied barns, an increase in Salmonella prevalence was observed, based on both bacteriologic and serologic analysis. Overall, there was an increase of 9.3% (P<0.05) in bacteriologic prevalence, and 25.1% (P<0.05) in serologic prevalence from “first pull” to “close out” groups. This study demonstrates that a significant increase of Salmonella prevalence occurs between the first and the last group of pigs from a finishing barn shipped to slaughter. In conclusion, “close out” groups of market pigs constitute a higher risk for Salmonella contamination of pork products.